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Introduction

AWS (Amazon Web Services) is the leading cloud platform, offering over 200 services for compute, storage, networking, and more. As a junior cloud engineer, you'll need foundational knowledge of core AWS services and cloud concepts to build and manage cloud infrastructure.

This guide covers essential interview questions for junior AWS cloud engineers, focusing on EC2, S3, VPC, IAM, and fundamental cloud concepts.

AWS EC2 (Elastic Compute Cloud)

1. What is AWS EC2 and what are its main benefits?

Answer: EC2 (Elastic Compute Cloud) provides resizable virtual servers in the cloud.

Key Benefits:

Elasticity: Scale up/down based on demand
Pay-as-you-go: Only pay for what you use
Variety: Multiple instance types for different workloads
Global: Deploy in multiple regions worldwide
Integration: Works seamlessly with other AWS services

Common Use Cases:

Web hosting
Application servers
Development/test environments
Batch processing
High-performance computing

Rarity: Very Common
Difficulty: Easy

2. Explain the difference between stopping and terminating an EC2 instance.

Answer:

Stopping an Instance:

Instance is shut down but not deleted
EBS root volume persists
You're charged for EBS storage
Can restart later with same configuration
Elastic IP remains associated
Instance ID stays the same

Terminating an Instance:

Instance is permanently deleted
EBS root volume deleted (unless configured otherwise)
No charges after termination
Cannot restart
Elastic IP is disassociated
Instance ID cannot be reused

# AWS CLI examples

# Stop an instance
aws ec2 stop-instances --instance-ids i-1234567890abcdef0

# Start a stopped instance
aws ec2 start-instances --instance-ids i-1234567890abcdef0

# Terminate an instance
aws ec2 terminate-instances --instance-ids i-1234567890abcdef0

Rarity: Very Common
Difficulty: Easy

AWS S3 (Simple Storage Service)

3. What is Amazon S3 and what are the different storage classes?

Answer: S3 is object storage for storing and retrieving any amount of data from anywhere.

Storage Classes:

Class	Use Case	Availability	Cost
S3 Standard	Frequently accessed data	99.99%	Highest
S3 Intelligent-Tiering	Unknown/changing access patterns	99.9%	Auto-optimized
S3 Standard-IA	Infrequently accessed	99.9%	Lower
S3 One Zone-IA	Infrequent, non-critical	99.5%	Lowest IA
S3 Glacier Instant	Archive, instant retrieval	99.9%	Very low
S3 Glacier Flexible	Archive, minutes-hours retrieval	99.99%	Very low
S3 Glacier Deep Archive	Long-term archive, 12hr retrieval	99.99%	Lowest

# Create S3 bucket
aws s3 mb s3://my-bucket-name

# Upload file
aws s3 cp myfile.txt s3://my-bucket-name/

# List objects
aws s3 ls s3://my-bucket-name/

# Download file
aws s3 cp s3://my-bucket-name/myfile.txt ./

Rarity: Very Common
Difficulty: Easy-Medium

AWS VPC (Virtual Private Cloud)

4. What is AWS VPC and what are its key components?

Answer: VPC is a logically isolated virtual network where you launch AWS resources.

Key Components:

Loading diagram...

Components:

Subnets: Segments of VPC IP range
- Public: Has route to Internet Gateway
- Private: No direct internet access
Internet Gateway: Enables internet access
NAT Gateway: Allows private subnet internet access (outbound only)
Route Tables: Control traffic routing
Security Groups: Instance-level firewall (stateful)
Network ACLs: Subnet-level firewall (stateless)

Rarity: Very Common
Difficulty: Medium

5. What's the difference between Security Groups and Network ACLs?

Answer:

Feature	Security Group	Network ACL
Level	Instance	Subnet
State	Stateful	Stateless
Rules	Allow only	Allow and Deny
Return Traffic	Automatic	Must be explicitly allowed
Application	Selective (per instance)	All instances in subnet
Rule Evaluation	All rules	Rules in order

Example:

# Create security group
aws ec2 create-security-group \
  --group-name web-sg \
  --description "Web server security group" \
  --vpc-id vpc-1234567890abcdef0

# Add inbound rule (allow HTTP)
aws ec2 authorize-security-group-ingress \
  --group-id sg-0123456789abcdef0 \
  --protocol tcp \
  --port 80 \
  --cidr 0.0.0.0/0

# Add inbound rule (allow SSH from specific IP)
aws ec2 authorize-security-group-ingress \
  --group-id sg-0123456789abcdef0 \
  --protocol tcp \
  --port 22 \
  --cidr 203.0.113.0/24

Rarity: Very Common
Difficulty: Medium

AWS IAM (Identity and Access Management)

6. Explain IAM users, groups, and roles.

Answer: IAM controls access to AWS resources.

IAM Users:

Individual identity with credentials
Long-term credentials (password, access keys)
Use for people or applications

IAM Groups:

Collection of users
Attach policies to groups
Users inherit group permissions

IAM Roles:

Temporary credentials
Assumed by users, applications, or services
No long-term credentials
Use for EC2 instances, Lambda functions, cross-account access

// Example IAM Policy (S3 read-only)
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:GetObject",
        "s3:ListBucket"
      ],
      "Resource": [
        "arn:aws:s3:::my-bucket",
        "arn:aws:s3:::my-bucket/*"
      ]
    }
  ]
}

Best Practices:

Use roles for EC2 instances (not access keys)
Follow least privilege principle
Enable MFA for privileged users
Rotate credentials regularly
Use groups for permission management

Rarity: Very Common
Difficulty: Medium

AWS Core Concepts

7. What are AWS Regions and Availability Zones?

Answer:

AWS Region:

Geographic location (e.g., us-east-1, eu-west-1)
Contains multiple Availability Zones
Isolated from other regions
Choose based on: latency, compliance, cost

Availability Zone (AZ):

One or more data centers within a region
Isolated from failures in other AZs
Connected with low-latency networking
Deploy across multiple AZs for high availability

Loading diagram...

High Availability Example:

# Launch instances in multiple AZs
aws ec2 run-instances \
  --image-id ami-0abcdef1234567890 \
  --instance-type t2.micro \
  --subnet-id subnet-1a \
  --count 1

aws ec2 run-instances \
  --image-id ami-0abcdef1234567890 \
  --instance-type t2.micro \
  --subnet-id subnet-1b \
  --count 1

Rarity: Very Common
Difficulty: Easy

8. What is an AMI (Amazon Machine Image)?

Answer: AMI is a template for creating EC2 instances.

Contains:

Operating system
Application server
Applications
Configuration settings

Types:

AWS-provided: Amazon Linux, Ubuntu, Windows
Marketplace: Third-party AMIs
Custom: Your own AMIs

Creating Custom AMI:

# Create AMI from running instance
aws ec2 create-image \
  --instance-id i-1234567890abcdef0 \
  --name "My-Web-Server-AMI" \
  --description "Web server with Apache configured"

# Launch instance from AMI
aws ec2 run-instances \
  --image-id ami-0abcdef1234567890 \
  --instance-type t2.micro \
  --key-name my-key-pair

Use Cases:

Standardized deployments
Backup and recovery
Auto Scaling
Multi-region deployment

Rarity: Common
Difficulty: Easy-Medium

AWS Storage

9. What is EBS and what are the different volume types?

Answer: EBS (Elastic Block Store) provides persistent block storage for EC2 instances.

Volume Types:

Type	Use Case	Performance	Cost
gp3 (General Purpose SSD)	Most workloads	3,000-16,000 IOPS	Lowest SSD
gp2 (General Purpose SSD)	Legacy, general use	Up to 16,000 IOPS	Low
io2/io1 (Provisioned IOPS)	Databases, critical apps	Up to 64,000 IOPS	Highest
st1 (Throughput Optimized HDD)	Big data, data warehouses	High throughput	Low
sc1 (Cold HDD)	Infrequent access	Lowest cost	Lowest

Creating and Attaching EBS:

# Create EBS volume
aws ec2 create-volume \
  --availability-zone us-east-1a \
  --size 100 \
  --volume-type gp3 \
  --iops 3000 \
  --throughput 125

# Attach to instance
aws ec2 attach-volume \
  --volume-id vol-1234567890abcdef0 \
  --instance-id i-1234567890abcdef0 \
  --device /dev/sdf

# Format and mount (on the instance)
sudo mkfs -t ext4 /dev/sdf
sudo mkdir /data
sudo mount /dev/sdf /data

# Make permanent (add to /etc/fstab)
echo "/dev/sdf /data ext4 defaults,nofail 0 2" | sudo tee -a /etc/fstab

EBS Snapshots:

# Create snapshot
aws ec2 create-snapshot \
  --volume-id vol-1234567890abcdef0 \
  --description "Backup before upgrade"

# Restore from snapshot
aws ec2 create-volume \
  --snapshot-id snap-1234567890abcdef0 \
  --availability-zone us-east-1a \
  --volume-type gp3

# Copy snapshot to another region
aws ec2 copy-snapshot \
  --source-region us-east-1 \
  --source-snapshot-id snap-1234567890abcdef0 \
  --destination-region us-west-2

Key Features:

Persistent: Data survives instance termination
Snapshots: Point-in-time backups to S3
Encryption: At-rest and in-transit
Resizable: Increase size without downtime
Multi-attach: io2 volumes can attach to multiple instances

Best Practices:

Use gp3 for most workloads (better price/performance)
Enable encryption by default
Regular snapshots for backups
Delete unused volumes to save costs

Rarity: Very Common
Difficulty: Easy-Medium

10. Explain S3 bucket policies and how they differ from IAM policies.

Answer: Both control access to S3, but they work differently:

IAM Policies:

Attached to users, groups, or roles
Control what identities can do
Managed centrally in IAM

S3 Bucket Policies:

Attached to S3 buckets
Control access to specific buckets
Can grant cross-account access
Can restrict by IP address

Example IAM Policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:GetObject",
        "s3:PutObject"
      ],
      "Resource": "arn:aws:s3:::my-bucket/*"
    }
  ]
}

Example S3 Bucket Policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "PublicReadGetObject",
      "Effect": "Allow",
      "Principal": "*",
      "Action": "s3:GetObject",
      "Resource": "arn:aws:s3:::my-public-bucket/*"
    },
    {
      "Sid": "RestrictByIP",
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:*",
      "Resource": [
        "arn:aws:s3:::my-bucket",
        "arn:aws:s3:::my-bucket/*"
      ],
      "Condition": {
        "NotIpAddress": {
          "aws:SourceIp": "203.0.113.0/24"
        }
      }
    }
  ]
}

Apply Bucket Policy:

# Create policy file (policy.json)
# Then apply it
aws s3api put-bucket-policy \
  --bucket my-bucket \
  --policy file://policy.json

# View current policy
aws s3api get-bucket-policy \
  --bucket my-bucket

# Delete policy
aws s3api delete-bucket-policy \
  --bucket my-bucket

Common Use Cases:

1. Public Website Hosting:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": "*",
      "Action": "s3:GetObject",
      "Resource": "arn:aws:s3:::my-website/*"
    }
  ]
}

2. Cross-Account Access:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::123456789012:root"
      },
      "Action": "s3:*",
      "Resource": [
        "arn:aws:s3:::shared-bucket",
        "arn:aws:s3:::shared-bucket/*"
      ]
    }
  ]
}

3. Enforce Encryption:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:PutObject",
      "Resource": "arn:aws:s3:::my-bucket/*",
      "Condition": {
        "StringNotEquals": {
          "s3:x-amz-server-side-encryption": "AES256"
        }
      }
    }
  ]
}

When to Use:

IAM Policy: Control what your users/applications can do
Bucket Policy: Control who can access your bucket (including external accounts)

Rarity: Very Common
Difficulty: Medium

Monitoring & Management

11. What is CloudWatch and how do you use it for monitoring?

Answer: CloudWatch is AWS's monitoring and observability service.

Key Components:

1. Metrics:

Numerical data points over time
EC2: CPU, Network, Disk
RDS: Connections, IOPS
Custom metrics: Application-specific

# View EC2 CPU metrics
aws cloudwatch get-metric-statistics \
  --namespace AWS/EC2 \
  --metric-name CPUUtilization \
  --dimensions Name=InstanceId,Value=i-1234567890abcdef0 \
  --start-time 2024-11-25T00:00:00Z \
  --end-time 2024-11-25T23:59:59Z \
  --period 3600 \
  --statistics Average,Maximum

# Publish custom metric
aws cloudwatch put-metric-data \
  --namespace MyApp \
  --metric-name PageLoadTime \
  --value 0.5 \
  --unit Seconds

2. Alarms:

# Create alarm for high CPU
aws cloudwatch put-metric-alarm \
  --alarm-name high-cpu-alarm \
  --alarm-description "Alert when CPU exceeds 80%" \
  --metric-name CPUUtilization \
  --namespace AWS/EC2 \
  --statistic Average \
  --period 300 \
  --threshold 80 \
  --comparison-operator GreaterThanThreshold \
  --evaluation-periods 2 \
  --dimensions Name=InstanceId,Value=i-1234567890abcdef0 \
  --alarm-actions arn:aws:sns:us-east-1:123456789012:my-topic

3. Logs:

# Create log group
aws logs create-log-group \
  --log-group-name /aws/application/myapp

# Create log stream
aws logs create-log-stream \
  --log-group-name /aws/application/myapp \
  --log-stream-name instance-1

# Put log events
aws logs put-log-events \
  --log-group-name /aws/application/myapp \
  --log-stream-name instance-1 \
  --log-events \
    timestamp=1234567890000,message="Application started" \
    timestamp=1234567891000,message="Processing request"

# Query logs
aws logs filter-log-events \
  --log-group-name /aws/application/myapp \
  --filter-pattern "ERROR" \
  --start-time 1234567890000

4. Dashboards:

# Create dashboard with boto3
import boto3
import json

cloudwatch = boto3.client('cloudwatch')

dashboard_body = {
    "widgets": [
        {
            "type": "metric",
            "properties": {
                "metrics": [
                    ["AWS/EC2", "CPUUtilization", {"stat": "Average"}]
                ],
                "period": 300,
                "stat": "Average",
                "region": "us-east-1",
                "title": "EC2 CPU Utilization"
            }
        },
        {
            "type": "metric",
            "properties": {
                "metrics": [
                    ["AWS/RDS", "DatabaseConnections"]
                ],
                "period": 300,
                "stat": "Sum",
                "region": "us-east-1",
                "title": "RDS Connections"
            }
        }
    ]
}

cloudwatch.put_dashboard(
    DashboardName='MyAppDashboard',
    DashboardBody=json.dumps(dashboard_body)
)

Common Monitoring Scenarios:

Monitor EC2 Instance:

# CPU, Network, Disk metrics are automatic
# For memory, need CloudWatch agent

# Install CloudWatch agent
wget https://s3.amazonaws.com/amazoncloudwatch-agent/amazon_linux/amd64/latest/amazon-cloudwatch-agent.rpm
sudo rpm -U ./amazon-cloudwatch-agent.rpm

# Configure agent (creates config file)
sudo /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-config-wizard

# Start agent
sudo /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl \
  -a fetch-config \
  -m ec2 \
  -s \
  -c file:/opt/aws/amazon-cloudwatch-agent/bin/config.json

Monitor Application Logs:

# Python application with CloudWatch logging
import boto3
import logging
from datetime import datetime

class CloudWatchHandler(logging.Handler):
    def __init__(self, log_group, log_stream):
        super().__init__()
        self.client = boto3.client('logs')
        self.log_group = log_group
        self.log_stream = log_stream
        
    def emit(self, record):
        log_entry = self.format(record)
        self.client.put_log_events(
            logGroupName=self.log_group,
            logStreamName=self.log_stream,
            logEvents=[{
                'timestamp': int(datetime.now().timestamp() * 1000),
                'message': log_entry
            }]
        )

# Usage
logger = logging.getLogger()
logger.addHandler(CloudWatchHandler('/aws/myapp', 'instance-1'))
logger.info("Application started")

Best Practices:

Set up alarms for critical metrics
Use log groups to organize logs
Create dashboards for quick overview
Set retention policies to control costs
Use metric filters for log analysis

Rarity: Very Common
Difficulty: Medium

Conclusion

Preparing for a junior AWS cloud engineer interview requires understanding core services and cloud concepts. Focus on:

EC2: Instance types, lifecycle, security
S3: Storage classes, bucket policies, versioning
VPC: Networking, subnets, security groups
IAM: Users, roles, policies, least privilege
Core Concepts: Regions, AZs, AMIs

Practice using the AWS Console and CLI to gain hands-on experience. Good luck!

Table of Contents

Junior Cloud Engineer AWS Interview Questions: Complete Guide

Introduction

AWS EC2 (Elastic Compute Cloud)

1. What is AWS EC2 and what are its main benefits?

2. Explain the difference between stopping and terminating an EC2 instance.

AWS S3 (Simple Storage Service)

3. What is Amazon S3 and what are the different storage classes?

AWS VPC (Virtual Private Cloud)

4. What is AWS VPC and what are its key components?

5. What's the difference between Security Groups and Network ACLs?

AWS IAM (Identity and Access Management)

6. Explain IAM users, groups, and roles.

AWS Core Concepts

7. What are AWS Regions and Availability Zones?

8. What is an AMI (Amazon Machine Image)?

AWS Storage

9. What is EBS and what are the different volume types?

10. Explain S3 bucket policies and how they differ from IAM policies.

Monitoring & Management

11. What is CloudWatch and how do you use it for monitoring?

Conclusion

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